1. Field of the Invention
This invention relates to a toner for use in the development of electrostatic latent images for electrophotographs, electrostatic recording, electrostatic printing, and the like. More particularly, this invention relates to a novel dry toner that contains calix (n) arene as a charge-control agent.
2. Description of the Prior Art
Electrostatic latent images can be made visible by the use of electrostatic attraction to cause the attachment of the toner thereto. As agents used to develop such latent electrostatic images, in addition to wet toners, there are dry toners, which are widely used.
In a system in which a dry toner is used to develop an electrostatic latent image, the most important factor is the static properties of the toner. A number of suggestions have been made concerning the control of the static properties of toner particles. In general, when toner is being made dyes, pigments, and charge-control agents are added as additives.
At present, the following techniques are in use. When the toner is positively charged, the nigrosine dye disclosed in Japanese Patent Publication No. 41-2427 or the quaternary ammonium salt disclosed in U.S. Pat. No. 4,654,175 can be used. When toner is negatively charged, the dye of complex salt containing metal disclosed in Japanese Patent Publication No. 45-26478, etc., can be used.
However, the structure of these charge-control agents is complex and their stability is poor. Therefore, the charge-control agents are degraded or decomposed by mechanical friction or impact, by changes in temperature, humidity, electrical impact, and by irradiation, so that they lose their charge-controlling ability.
In recent years, a variety of charge-control agents to solve these problems have been disclosed, for example, in U.S. Pat. Nos. 4,206,064 and 4,656,112, in which metal complexes of salicylic acid and zinc complexes of aromatic oxycarboxylic acid disclosed can be used.
However, these compounds are colored or contain heavy metals such as chrome, cobalt, copper, zinc, etc., which are unsuitable as toner additives.
Japanese Laid-Open Patent Publication No. 63-266462 discloses toners that contain, for example, compounds known to act as developer, sensitizers, antioxidation agents, or the like to prevent deterioration of the surface-treatment carrier (a phenomenon in which the toner comes to be spent on the surface of the carrier, which damages the static properties) in a binary dry developing agent. As antioxidation agents, there are, for example, alkylated derivatives of compounds such as 2,6-di-tert-butyl-p-cresol, 2,6-di-tert-butyl-4-ethylphenol, and hydroquinones, the alkylated derivatives containing 1 to 5 carbon atoms in the alkyl group; 2,2'-methylene-bis-(4-methyl- 6-tert-butylphenol); and 2,2'-methylene-bis-(4-ethyl-6-tert-butylphenol).
In this way, various suggestions have been made to improve the quality of toners. However, conventional toners are disadvantageous in that the charge control changes with environmental changes such as in the temperature and humidity, the stability of toner is poor when it is preserved for a long period of time, and the static properties of toner are also poor, so charge-control agents that confer strong static properties and that are superior in heat-resistance are needed, so as to be usable in a variety of copying machines.
This invention was accomplished by the discovery of an excellent charge-control agent, calix (n) arene compounds, that overcomes the defects of conventional charge-load agents.
For the making of calix (n) arene, phenol and formaldehyde are the starting materials, and the yield is high when synthesis is done with a concentrated alkali. These compounds have a cylindrical structure that resembles that of cyclodextrin.
In the report of Zinke et al. (Ber. dtsch. chem. Ges., 74, 1792, (1941)) it was found that a substance with a high melting point can be obtained by the reaction of phenol and formaldehyde in the presence of sodium hydroxide. Gutsche et al. have published a detailed report of the preparation of various kinds of calix (n) arene derivatives and of their structures and properties (J. Am. Chem. Soc. 103, 3782, (1981)).
Calix (n) arene derivatives may be put to practical use as clathrate compounds in enzyme reaction and catalyzed reactions, or in the transport of metal ions (as disclosed in, for example, Japanese Laid-Open Patent Publication Nos. 61-291546, 62-65250, 63-72669, 63-99031, 63-99035, 62-136242, and 63-7837).
However, it has not been disclosed until now that it is possible to use calix (n) arene compounds as a charge-control agent in electrostatic developing toner.